1. Field of the Invention
The present invention relates to a method for the production of films, in particular, optically high-quality, weather-and fracture-resistant protective and decorative films, which contain, in at least one layer, mixtures of fluorine polymers and poly(meth)acrylates. The invention also relates to a method of providing substrates with the polymer film of the invention.
2. Description of the Background
Films which contain mixtures of fluorine polymers and poly(meth)acrylates are widely known in technical circles. In particular, PVDF/PMMA blends have excellent characteristics, which are clearly better than those of the individual components, if these polymers are mixed in the right ratio. Thus, the pronounced crystallinity of the PVDF can be reduced by an addition of at least 25% poly(meth)acrylate to a degree which no longer negatively influences the optical characteristics of the film. The addition of at least 40% PVDF to poly(meth)acrylate leads to a clear increase in chemical resistance of the film. If at least 55% PVDF is added, then the low-temperature tenacity is, over and above that, also improved.
Up to now, films made of these mixtures have been either cast from organic solution onto carrier films or extrusion-coated on carrier films as a melt.
The first method incurs high investment costs, since the solvents needed, such as N-methylpyrrolidone, impose a significant environmental hazard. Therefore, a release of these solvents into the surrounding environment must be avoided to the greatest extent possible. Moreover, the rates at which the films can be produced by this method are relatively low. Therefore, this method is, as a whole, very expensive.
A second way to produce these films is to extrude a film onto a carrier film, as is described in World Patent No. 96/40480. The disadvantage in this method is that the carrier film must possess a relatively high heat resistance, since otherwise, it is deformed by the hot melt, as is described, for example, in Example 2 of World Patent No. 96/40480. Accordingly, one cannot dispense with the use of relatively expensive carrier films in the production of multilayer PVDF/PMMA films. In the production of monolayer PVDF/PMMA films, this method is, moreover, expensive, since the carrier layer must be removed. Moreover, the carrier layer is joined with the PVDF/PMMA when hot. This results in additional disadvantages. In particular, the haze values are impaired by this measure.
Attempts to produce PVDF/PMMA films without a carrier film are known. These films, however, are hazy and do not have the desired surface gloss. A need, therefore, continues to exist for a method of preparing improved PVDF/PMMA films.
Accordingly, one object of the present invention is to provide a method of producing films which contain at least one layer of mixtures of fluorine polymers and poly(meth)acrylates and with which monolayer fluorine polymer- and poly(meth)acrylate-containing, optically high-quality, weather- and fracture-resistant films can be produced, without having to use solvents or having to coat carrier films when hot.
Another object of the invention is to provide as low-cost a method as possible of producing such polymer films.
Still another object of the invention is to provide a solvent-free method in which films with a particularly low haze, which contain at least one layer of poly(meth)acrylate and fluorine polymers, are produced.
Yet another object of the present invention is to provide a method for the production of films of the above type, which make possible high web travel rates.
Briefly, these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by a method of producing films containing at least one layer of fluorine polymers and poly(meth)acrylates comprising (i) preparing a mixture of fluorine polymer and poly(meth)acrylate; and (ii) extruding the mixture maintained below its gel-forming temperature through the die of an extruder having a filter placed before entry of the mixture into the die, the temperature of the die being maintained higher than the temperature of the composition upon entry into the die but lower than the gel-forming temperature of the mixture, onto a roll having a temperature xe2x89xa6100xc2x0 C., thereby forming said at least one layer in the shape of a film.